866 research outputs found
Quantum ballistic experiment on antihydrogen fall
We study an interferometric approach to measure gravitational mass of
antihydrogen. The method consists of preparing a coherent superposition of
antihydrogen quantum state localized near a material surface in the
gravitational field of the Earth, and then observing the time distribution of
annihilation events followed after the free fall of an initially prepared
superposition from a given height to the detector plate. We show that a
corresponding time distribution is related to the momentum distribution in the
initial state that allows its precise measurement. This approach is combined
with a method of production of a coherent superposition of gravitational states
by inducing a resonant transition using oscillating gradient magnetic field. We
estimate an accuracy of measuring the gravitational mass of antihydrogen atom
which could be deduced from such a measurement.Comment: arXiv admin note: text overlap with arXiv:1403.478
Quantum reflection of antihydrogen from nanoporous media
We study quantum reflection of antihydrogen atoms from nanoporous media due
to the Casimir-Polder (CP) potential. Using a simple effective medium model, we
show a dramatic increase of the probability of quantum reflection of
antihydrogen atoms if the porosity of the medium increases. We discuss the
limiting case of reflections at small energies, which have interesting
applications for trapping and guiding antihydrogen using material walls
Properties of nanostructured diamond-silicon carbide composites sintered by high pressure infiltration technique
A high-pressure silicon infiltration technique was applied to sinter diamondâSiC composites with different diamond crystal sizes. Composite samples were sintered at pressure 8 GPa and temperature 2170 K. The structure of composites was studied by evaluating x-ray diffraction peak profiles using Fourier coefficients of ab initio theoretical size and strain profiles. The composite samples have pronounced nanocrystalline structure: the volume-weighted mean crystallite size is 41â106 nm for the diamond phase and 17â37 nm for the SiC phase. The decrease of diamond crystal size leads to increased dislocation density in the diamond phase, lowers average crystallite sizes in both phases, decreases composite hardness, and improves fracture toughness
Quantum reflection of antihydrogen from Casimir potential above matter slabs
We study quantum reflection of antihydrogen atoms from matter slabs due to
the van der Waals/Casimir-Polder (vdW/CP) potential. By taking into account the
specificities of antihydrogen and the optical properties and width of the slabs
we calculate realistic estimates for the potential and quantum reflection
amplitudes. Next we discuss the paradoxical result of larger reflection
coefficients estimated for weaker potentials in terms of the Schwarzian
derivative. We analyze the limiting case of reflections at small energies,
which are characterized by a scattering length and have interesting
applications for trapping and guiding antihydrogen using material walls
Gravitational resonance spectroscopy with an oscillating magnetic field gradient in the GRANIT flow through arrangement
Gravitational resonance spectroscopy consists in measuring the energy
spectrum of bouncing ultracold neutrons above a mirror by inducing resonant
transitions between different discrete quantum levels. We discuss how to induce
the resonances with a flow through arrangement in the GRANIT spectrometer,
excited by an oscillating magnetic field gradient. The spectroscopy could be
realized in two distinct modes (so called DC and AC) using the same device to
produce the magnetic excitation. We present calculations demonstrating the
feasibility of the newly proposed AC mode
Frequency shifts in gravitational resonance spectroscopy
Quantum states of ultracold neutrons in the gravitational field are to be
characterized through gravitational resonance spectroscopy. This paper
discusses systematic effects that appear in the spectroscopic measurements. The
discussed frequency shifts, which we call Stern-Gerlach shift, interference
shift, and spectator state shift, appear in conceivable measurement schemes and
have general importance. These shifts have to be taken into account in
precision experiments
Antiproton-Hydrogen annihilation at sub-kelvin temperatures
The main properties of the interaction of ultra low-energy antiprotons ( a.u.) with atomic hydrogen are established. They include the
elastic and inelastic cross sections and Protonium (Pn) formation spectrum. The
inverse Auger process () is taken into account in the
framework of an unitary coupled-channels model. The annihilation cross-section
is found to be several times smaller than the predictions made by the black
sphere absorption models. A family of nearthreshold metastable
states is predicited. The dependence of Protonium formation probability on the
position of such nearthreshold S-matrix singularities is analysed. An
estimation for the annihilation cross section is obtained.Comment: latex.tar.gz file, 22 pages, 9 figure
Whispering Gallery States of Antihydrogen
We study theoretically interference of the long-living quasistationary
quantum states of antihydrogen atoms, localized near a concave material
surface. Such states are an antimatter analog of the whispering gallery states
of neutrons and matter atoms, and similar to the whispering gallery modes of
sound and electro-magnetic waves. Quantum states of antihydrogen are formed by
the combined effect of quantum reflection from van der Waals/Casimir-Polder
(vdW/CP) potential of the surface and the centrifugal potential. We point out a
method for precision studies of quantum reflection of antiatoms from vdW/CP
potential; this method uses interference of the whispering gallery states of
antihydrogen.Comment: 13 pages 7 figure
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